(approximately
5,000 grams) to a constant weight at110°C.
Then cool the sample for 1 to 3 hours, immerseit
in water, and allow it to soak for about 24 hours.

2. Remove the sample from the water and dry it to

a
saturated, surface-dry condition by rolling the samplein
an absorbent cloth until visible films of water areremoved
and the particle surfaces appear slightly damp.

3. Weigh the sample in the SSD condition and

record
the weight to the nearest 0.5 gram. Thenimmediately
place the sample into a container or wirebasket
and determine its immersed weight (or weight in water) at 23°C. Be sure that
any entrapped air is removed by shaking the container or basket while it is
immersed. Record the immersed weight to the nearest 0.5 gram.

4. Dry the sample to a constant weight at 110°C,

cool
it for 1 to 3 hours, and then weigh the oven-driedsample.
Record the weight to the nearest 0.5 gram.

5. The bulk specific gravity (SSD condition) and

the
percentage of absorption can now be calculatedusing
the following formulas:

And:

Where:

A= weight of oven-dried sample
in air (ingrams)

B= weight of SSD sample in air
(in grams)

C= immersed weight of saturated sample (in grams)

Specific Gravity and Absorption, Fine Aggregate

(ASTM
C 128).— The
procedures for determining thebulk
specific gravity of the fine aggregate in a SSDcondition
and the percentage of absorption are asfollows:

1. Dry a representative sample of the fine

aggregate
(about 1,000 grams) to a constant weight at110°C.
Then cool the sample, immerse it in water, andallow
it to soak for about 24 hours.

3. Next, you place a water-absorption cone (fig. 13-18) large end down on a
smooth surface and fill it loosely with the aggregate. Then lightly tamp the
surface of the aggregate 25 times with the metal tamper.

4. Lift the cone vertically from the sand and observe
the action of the sample. If it retains its conical shape, free moisture is
present and continued drying (Step 2) followed by repeated tamping (Step 3) is
required. If the sample slumps slightly, the fine aggregate has reached the
desired SSD condition.

5. Weigh exactly 500 grams of the SSD sample and place it in a partially
water-filled pycnometer top-and-jar assembly (fig. 13-19). Fill the jar with
additional water to approximately 90 percent of its capacity.

6. Agitate the sample in the pycnometer assembly
to remove any entrapped air, adjust the water temperature to 23°C, and fill the
pycnometer to its calibrated capacity. Then weigh the filled pycnometer to the
nearest 0.1 gram and record the weight.

7. Remove the sample from the pycnometer and
dry
it to a constant weight at 110°C. Then cool the

sample
in air for about 1 hour and weigh it. Recordthis
weight to the nearest 0.1 gram.

8. Determine the weight of the pycnometer filled

to
its calibrated capacity with water at 23° + 1.7°C.Record
this weight.

9. You can now calculate the specific gravity of

the
SSD fine aggregate and the percentage ofabsorption
by using the following formulas:

And:

Where:

A

= weight of the
oven-dried specimen in air (ingrams)

B

= weight of
pycnometer filled with water (ingrams)

C

= weight of
pycnometer, sample, and water (ingrams)

Surface Moisture (ASTM C 70 and ASTM C

566).—
A summary of the ASTM
procedures used todetermine
the total moisture content and the

Figure 13-18.—Water-absorption cone and

tamper.

Figure 13-19.—Pycnometer top-and-jar

assembly.

percentage of surface moisture in either fine or coarse

aggregate
are as follows:

1. Secure and weigh a sample of the aggregate

that
is representative of the moisture content of thematerial
being tested.

2. Dry the sample to a constant weight at 110°C. You should take care to
avoid loss of material during testing. The sample is thoroughly dry when further
heating causes, or would cause, less than 0.1 percent additional loss in weight.

3. Weigh and record the weight of the oven-dried

sample.

4.

Calculate the total
moisture contentusing thefollowing formula:

Where:

P =

total moisture
content (percent)

W=

weight of original
sample (in grams)

D =

weight of
oven-dried sample (in grams)

The surface moisture is equal to
the difference between the total moisture content and the absorption. An
alternate determination of surface moisture in fine aggregate is obtained by
displacement as follows:

1. Select a representative sample of the fine aggregate
weighing not less than 200 grams.

available
to improve workability, increase resistance tofreezing
and thawing, and compensate for inadequatecuring
time and conditions.

Accelerators

Sometimes it is desirable to accelerate the hydration

reactions.
The result is a high-early strength and a higherrate
of heat production. This combination can be useful in winter operations. The
addition of a chemical accelerator (generally calcium chloride) to the mix will
produce the desired conditions. The amount specified is usually 2 percent of the
weight of cement and rarely more than 3 percent. The main reaction with calcium
chloride occurs within the first 3 days. The ultimate strength of concrete is
not affected by the use of this chemical.

Retarders

Retarders are used when excessively high heat and too rapid setting of
concrete would prevent full hydration. Many materials retard setting of
concrete. Basically, these materials are types of fatty acids, starches, or
sugars.